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Date:   Thu, 15 Sep 2022 15:19:33 +0200
From:   Marco Felsch <m.felsch@pengutronix.de>
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     mchehab@kernel.org, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, vkoul@kernel.org, kishon@ti.com,
        sakari.ailus@linux.intel.com, hverkuil@xs4all.nl,
        jacopo@jmondi.org, linux-kernel@vger.kernel.org,
        linux-phy@lists.infradead.org, devicetree@vger.kernel.org,
        linux-media@vger.kernel.org, kernel@pengutronix.de
Subject: Re: [PATCH 3/4] media: dt-bindings: add bindings for Toshiba TC358746
Message-ID: <20220915131933.wclmhtliji5wz35t@pengutronix.de>
References: <20220818143307.967150-1-m.felsch@pengutronix.de>
 <20220818143307.967150-4-m.felsch@pengutronix.de>
 <YxUoSfbrPPPT5nz6@pendragon.ideasonboard.com>
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Hi Laurent,

On 22-09-05, Laurent Pinchart wrote:
> Hi Marco,
> 
> Thank you for the patch.
> 
> On Thu, Aug 18, 2022 at 04:33:06PM +0200, Marco Felsch wrote:
> > Add the bindings for the Toshiba TC358746 Parallel <-> MIPI-CSI bridge
> > driver.
> > 
> > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > ---
> >  .../bindings/media/i2c/toshiba,tc358746.yaml  | 157 ++++++++++++++++++
> >  1 file changed, 157 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > new file mode 100644
> > index 000000000000..9783cca363c6
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.yaml
> > @@ -0,0 +1,157 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/media/i2c/toshiba,tc358746.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Toshiba TC358746 Parallel to MIPI CSI2 Bridge
> > +
> > +maintainers:
> > +  - Marco Felsch <kernel@pengutronix.de>
> > +
> > +description: |-
> > +  The Toshiba TC358746 converts a parallel video stream into a MIPI CSI-2
> > +  stream. The direction can be either parallel-in -> csi-out or csi-in ->
> > +  parallel-out The chip is programmable trough I2C and SPI but the SPI
> > +  interface is only supported in parallel-in -> csi-out mode.
> > +
> > +  Note that the current device tree bindings only support the
> > +  parallel-in -> csi-out path.
> > +
> > +properties:
> > +  compatible:
> > +    const: toshiba,tc358746
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  clocks:
> > +    description:
> > +      The phandle to the reference clock source. This corresponds to the
> > +      hardware pin REFCLK.
> > +    maxItems: 1
> > +
> > +  clock-names:
> > +    const: refclk
> 
> As there's a single clock, should we omit the clock name ?

Don't know, I would rather keep it to make it explicite. Many other go
that way too.

> > +# The bridge can act as clock provider for the sensor. To enable this support
> > +# #clock-cells must be specified. Attention if this feature is used than the
> 
> s/than/then/

Sure, thanks.

> 
> > +# mclk rate must be at least: (2 * link-frequency) / 8
> > +#                             `------------------?   ^
> > +#                             internal PLL rate   smallest possible mclk-div
> 
> Could this be captured in the description of the property instead of a
> comment ?

Hm.. a few (1,2) bindings using comments like this but I'm not against
it. If it belongs to the description, which property should I use? Since
there is no: clock-controller property like gpio-controller or
interrupt-controller. The clock provider will be activated based on the
#clock-cells property. But this property has nothing to with the
description since this property specifies the cell size.

> > +  "#clock-cells":
> > +    const: 0
> > +
> > +  clock-output-names:
> > +    description:
> > +      The clock name of the MCLK output, the default name is tc358746-mclk.
> > +    maxItems: 1
> > +
> > +  vddc-supply:
> > +    description: Digital core voltage supply, 1.2 volts
> > +
> > +  vddio-supply:
> > +    description: Digital I/O voltage supply, 1.8 volts
> > +
> > +  vddmipi-supply:
> > +    description: MIPI CSI phy voltage supply, 1.2 volts
> > +
> > +  reset-gpios:
> > +    description:
> > +      The phandle and specifier for the GPIO that controls the chip reset.
> > +      This corresponds to the hardware pin RESX which is physically active low.
> > +    maxItems: 1
> > +
> > +  ports:
> > +    $ref: /schemas/graph.yaml#/properties/ports
> > +    properties:
> > +      port@0:
> > +        $ref: /schemas/graph.yaml#/properties/port
> > +        description: Input port
> 
> Are the H/V sync signal polarities fixed, or should they be specified
> here ?

At the moment they are fixed. I can describe it if you want.

> Does the chip support external sync only, or also BT.656 ? In the
> latter case this needs a bus-type.

Yes, the chip also supports BT.656 but the driver doesn't support it
yet. You're right, that we should make it explicite albeit it would a
bit overhead yet since the only mode is: parallel-in with externa syncs.

> > +
> > +      port@1:
> > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > +        description: Output port
> > +
> > +        properties:
> > +          endpoint:
> > +            $ref: /schemas/media/video-interfaces.yaml#
> > +            unevaluatedProperties: false
> > +
> > +            properties:
> > +              data-lanes:
> > +                minItems: 1
> > +                maxItems: 4
> > +
> > +              clock-noncontinuous: true
> > +              link-frequencies: true
> > +
> > +            required:
> > +              - data-lanes
> > +              - link-frequencies
> > +
> > +    required:
> > +      - port@0
> > +      - port@1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - clocks
> > +  - clock-names
> > +  - vddc-supply
> > +  - vddio-supply
> > +  - vddmipi-supply
> > +  - ports
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +
> > +    i2c {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      csi-bridge@e {
> > +        compatible = "toshiba,tc358746";
> > +        reg = <0xe>;
> > +
> > +        clocks = <&refclk>;
> > +        clock-names = "refclk";
> > +
> > +        reset-gpios = <&gpio 2 GPIO_ACTIVE_LOW>;
> > +
> > +        vddc-supply = <&v1_2d>;
> > +        vddio-supply = <&v1_8d>;
> > +        vddmipi-supply = <&v1_2d>;
> > +
> > +        /* sensor mclk provider */
> > +        #clock-cells = <0>;
> > +
> > +        ports {
> > +          #address-cells = <1>;
> > +          #size-cells = <0>;
> > +
> > +          /* Input */
> > +          port@0 {
> > +            reg = <0>;
> > +            tc358746_in: endpoint {
> > +              remote-endpoint = <&sensor_out>;
> > +              };
> 
> Wrong indentation here.

Yes, thanks.

Regards,
  Marco

> > +          };
> > +
> > +          /* Output */
> > +          port@1 {
> > +            reg = <1>;
> > +            tc358746_out: endpoint {
> > +              remote-endpoint = <&mipi_csi2_in>;
> > +              data-lanes = <1 2>;
> > +              clock-noncontinuous;
> > +              link-frequencies = /bits/ 64 <216000000>;
> > +            };
> > +          };
> > +        };
> > +      };
> > +    };
> 
> -- 
> Regards,
> 
> Laurent Pinchart
>